It is customary when writing sheet music for bowed musical instruments to specify the direction of bowing of each note or passage to ensure consistency of interpretation and correct articulation of the musical phrases thus annotated.
Devices capable of writing sheet music automatically in response to a tone signal from a musical instrument are known in the prior art. When a musical passage played on a bowed instrument is recorded onto sheet music using a device capable of such operation automatically, it is desirable to obtain a partition containing the bowing information along with the rest of the musical notation. This has not been the case in the past and bowing information was either lost or written in manually after the fact with the inherent possibility of error from the lack of simultaneity of the events.
The mechanics of bowing and the related motional behavior of bowed vibrating elements in musical instruments are known in the prior art.
When a bow is drawn across a vibrating element to produce a musical tone, the gripping surface of the bow displaces the vibrating element in the direction of bowing at a relatively low speed until a limit is reached where the friction between the contacting surfaces becomes insufficient to displace the vibrating element further in that direction.
If the bow continues to move in the direction of bowing, the vibrating element slips under the bow in the opposite direction at a relatively high speed until a point is reached where the elasticity limits of the vibrating element force it to stop, and the forces of friction between the surfaces are once again sufficient to pull the vibrating element in the direction of bowing and start another similar cycle of vibration for as long as the bow is drawn across the vibrating element with sufficient speed and contact pressure to maintain the tone.
A transducer responsive to the above-mentioned displacements of a vibrating element in the plane of bowing produces a tone signal, the waveform of which resembles a sawtooth. The most vertical slope of each cycle of this waveform corresponds to the sudden slipping of the vibrating element under the bow.
This characteristic of each cycle of the tone signal appears consistently upon bowing and is independent of which note is being played.
It is therefore an object of the present invention to detect the polar direction of this rapid voltage change which is directly related to the direction of bowing, irrespectively of the frequency of the played note.
It is a further object of the present invention to produce an indication of the detection in the form of a signal, the magnitude of which is independent of the amplitude or frequency of the signal from the transducer.
It is a still further object of the present invention to provide an indication of the direction of bowing for the entire duration of the note or passage being played, including the period during which the bow leaves the vibrating element in a state of free vibration at the end of a bow stroke.